Electronic component protection power supply clamp circuit

ABSTRACT

Electronic component protection power supply clamp circuits comprising a plurality of p-type channel metal-oxide-semiconductor (PMOS) and n-type channel metal-oxide-semiconductor (NMOS) transistors are described. These clamp circuits use a feedback latching circuit to retain an electrostatic discharge (ESD)-triggered state and efficiently conduct ESD current that has been diverted into the power supply, in order to dissipate ESD energy. The feedback latching circuit also maintains a clamp transistor in its off state if the clamp circuit powers up untriggered, thus enhancing the clamp circuit&#39;s immunity to noise during normal operation. Passive resistance initialization of key nodes to an untriggered state, as well as passive resistance gate input loading of a large ESD clamping transistor, further enhances the clamp circuit&#39;s immunity to false triggering. This also lengthens the time that the clamp circuit remains in the ESD-triggered state during human body model (HBM) or other long duration detected ESD events.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/004,970, filed Jan. 12, 2011, which is incorporated by reference asif fully set forth.

FIELD OF INVENTION

The present invention is generally directed to protection supply clampcircuits used to dissipate electrostatic discharge (ESD) energy withoutcausing damage to electronic components.

BACKGROUND

Electronic components are typically tested to determine whether theymeet various electrostatic discharge (ESD) qualification specificationsin order to demonstrate that they will be reliable under ESD conditionsto which they may be exposed during manufacturing and handling. ESDexposure may change the electrical characteristics of the components,which may include semiconductor devices, (e.g., integrated circuits(ICs)), that typically have multiple terminals, (e.g., pads, bumps,balls, pins), as well as a package frame or lid, that either directly orindirectly connect to at least one of a power supply, a digital circuit,an analog circuit, or any other external circuit or device.

For an electronic component that resides on, or is cut from, asemiconductor wafer, or is contained in a component package, ESD currentmay flow between two or more connection points of the electroniccomponent. When the ESD current flows between positive and negativepower supply terminals, a supply clamp circuit may be used to dissipateESD energy directly, thus preventing ESD-induced voltages from damagingthe electronic component. A supply clamp circuit typically uses alow-resistance path to shunt ESD current.

When ESD current flows through circuit connections other than the powersupply terminals, such as from an input or output (I/O) signal line, itis common practice to divert the ESD current through one or more diodesconnected from the I/O signal line to one of the power supply terminals.Upon reaching the power supply, the power supply clamp circuit conductsESD current through a low-resistance path between the power supplyterminals to limit the supply voltage, thus protecting the electroniccomponent from being damaged.

Therefore, supply clamp circuits internal to an electronic component areconfigured to respond to ESD events and provide a safe path for thedissipation of ESD current. These supply clamp circuits are configuredto discriminate between an ESD event, where a clamp transistor is usedto provide a low-resistance path to shunt ESD current, and a normalsupply powered or ramp-up operation, where the clamp transistor mustremain deactivated (i.e., off) and in a low-current state. A supplyclamp circuit that employs a function that latches itself into anESD-event state upon detection of ESD exposure must not be falselytriggered in response to a normal power-on operating condition.Otherwise, the supply clamp circuit may be damaged by the unlimitedenergy of an active power supply.

In non-latching designs, a resistor-capacitor (RC) circuit may be usedto detect an ESD event and activate the clamp transistor to provide alow-resistance supply short to dissipate the ESD energy in a safemanner. In the most classic design, an RC timer remains enabled for thefull duration of the ESD event state; (e.g., approximately 2microseconds). The RC time constant must also be substantially shorterthan the time over which a power supply ramps up to its static level innormal operation; (e.g., 10 microseconds or larger).

In configurations of supply clamp circuits that do not latch themselvesinto a lower resistance state after detecting an ESD event, a very largeRC time constant is required, (e.g., 1 to 2 microseconds), to continueclamping until ESD energy is completely dissipated. Supply clampcircuits designed in this manner require an RC circuit that occupies avery large chip (die) area. Such supply clamp circuits are susceptibleto failure if the leakage current through the capacitor in the RCcircuit is large. In contrast, supply clamp circuits that latch into anESD-event-detected state can use much smaller RC time constants, sincethey must only differentiate the rate of the supply ramp between anormal power supply ramp-up operation and an ESD event state. When ESDis discharged through a circuit supply terminal, the ramp rate isgenerally under 100 nanoseconds, while the rate for a normal powersupply ramp-up operation is typically 10 microseconds or larger. An ESDcircuit with a latching mechanism needs only to detect the leading edgeof the ESD event, after which the circuit latches itself into a stateindicating an ESD event has been detected, and clamps for as long as anESD state persists. Thus, there is no long-duration RC timer expirationthat determines ESD event end time. Instead, a loss of latched ESDstate, due to a mostly collapsed supply voltage, stops any furtherclamping from occurring.

The latching mechanism in this modified design is typically formedthrough a feedback circuit, which maintains the clamp in its lowresistance state until the ESD event has been dissipated. Thedisadvantage of the latching approach is that the supply clamp circuitbecomes susceptible to catastrophic damage if it is falsely triggeredunder normal operating conditions, since the power supply will continueto provide current into the electronic component and the feedbackcircuit would never allow the clamp transistor to shut off. As a result,the trigger and feedback circuit must be immune to false triggering overa wide range of conditions, including: 1) power supply ramp time andfinal voltage level; 2) temperature; 3) power supply noise or ripple; 4)device manufacturing tolerances: resistor, capacitor, n-type channelmetal-oxide-semiconductor (NMOS) and p-type channelmetal-oxide-semiconductor (PMOS) process variations; and 5) agingeffects, such as negative or positive bias temperature instability,(negative gate bias voltage temperature instability (NBTI) or positivegate bias voltage temperature instability (PBTI)), which cause a shiftin transistor threshold voltage when a non-zero gate voltage occurs overa long time period.

FIGS. 1 and 2 show two examples of conventional electronic componentprotection power supply clamp circuits that are connected across a powersupply used by an electronic component that typically includes atransistor circuit. Multiple instances of these power supply clampcircuits may be used to handle a particular current.

In FIG. 1, a conventional electronic component protection power supplyclamp circuit 100 is shown that includes capacitors 102 and 104, aresistor 106, a diode 108, PMOS transistors 110, 112 and 114, and NMOStransistors 116, 118 and 120. Each of these components is connected toat least one of a negative power supply terminal (Vss) 122 or a positivepower supply terminal (Vdd) 124. The PMOS transistor 110 includes a gateterminal 126, a source terminal 128 and a drain terminal 130. PMOStransistor 112 includes a gate terminal 132, a source terminal 134 and adrain terminal 136. PMOS transistor 114 includes a gate terminal 138, asource terminal 140 and a drain terminal 142. NMOS transistor 116includes a gate terminal 144, a source terminal 146 and a drain terminal148. NMOS transistor 118 includes a gate terminal 150, a source terminal152 and a drain terminal 154. NMOS transistor 120 serves as a clamptransistor that includes a gate terminal 156, a source terminal 158 anda drain terminal 160. The source terminals 146, 152 and 158 areconnected to Vss 122. The source terminals 128, 134 and 140, and thedrain terminal 160, are connected to Vdd 124.

As shown in FIG. 1, capacitor 102 is connected between Vdd supply 124and a node 162. The capacitor 104 is connected between Vdd 124 and anode 164. The resistor 106 is connected between Vss 122 and the node162. The diode 108 includes an anode 166 that is connected to Vss 122,and a cathode 168 that is connected to Vdd 124. The node 162 is alsoconnected to the gate terminal 132 of the PMOS transistor 112, the gateterminal 144 of the NMOS transistor 116 and the drain terminal 130 ofPMOS transistor 110. The node 164 is also connected to the drainterminal 136 of PMOS transistor 112, the drain terminal 148 of NMOStransistor 116, the gate terminal 126 of the PMOS transistor 110, thegate terminal 138 of the PMOS transistor 114, and the gate terminal 150of NMOS transistor 118. A node 170 connects together the drain terminal142 of the PMOS transistor 114, the drain terminal 154 of the NMOStransistor 118 and the gate terminal 156 of the NMOS transistor 120.

In the circuit 100 of FIG. 1, a “latch” is essentially formed by twoinverters: a first inverter 172 including the transistors 112 and 116,and a second inverter 174 including the transistor 110, which providesinversion for only one polarity. Thus, the inverters 172 and 174 runback-to-back, whereby each inverter 172 and 174 feeds the other's input,thus constituting a latch configuration 172/174. The resistor 106assures that the voltage input on node 162 starts out by feeding a logiclow voltage to the gates 132 and 144 of the inverter 172. As the powersupply providing Vss 122 and Vdd 124 ramps up in response to theoccurrence of an ESD event, the output of the latch configuration172/174 (i.e., node 164) serves as latch feedback to cause latching tooccur. During an ESD event where the power supply ramps up very rapidly,the capacitor 102 does not develop any significant voltage drop, thuscausing a short circuit to form between the power supply and theinverter 172. Thus, an output low on node 164, which turns on thetransistor 110 in the inverter 174, causes the voltage across thecapacitor 102 to remain substantially at zero, thus latching the ESDevent.

In addition, the transistors 114 and 118 form a third inverter 176,which feeds a logic high voltage to the gate 156 of the transistor 120to clamp, (i.e., short circuit), the power supply in order to keep theVdd 124 from going too high. The diode 108 deals with ESD current due toreverse supply polarity. For such ESD reverse current, the diode 108 isforward-biased to safely limit the supply voltage.

In FIG. 2, an alternative conventional electronic component protectionpower supply clamp circuit 200 is shown that includes capacitors 202 and204, a resistor 206, a diode 208, PMOS transistors 210, 212 and 214, andNMOS transistors 216, 218, 220, 222 and 224. The circuit 200 hastransposed the RC circuit formed by the capacitor 202 and the resistor206 with a corresponding latch inverter as NMOS transistor 216.Operation of the circuit 200 is similar to that of the circuit 100 ofFIG. 1, except that the polarity of the RC and feedback stages isreversed. The addition of a third inverter formed by the transistors 214and 222 may be beneficial in some cases by enabling a reduction in thesize of the inverter formed by the transistors 210 and 218, and thefeedback transistor 216.

The problem with the circuit 100 of FIG. 1 is that there is no assurancethat node 164 will follow the power supply as it ramps up in preparationfor normal operation. A normal supply ramp is so slow, (e.g., on theorder of 10 microseconds or slower), that the capacitors 102 and 104 mayexhibit the characteristics of an open circuit due to the RC timeconstant of the resistor 106 and the capacitor 102. Thus, node 162should remain at the Vss 122 potential during a normal power supplyramp-up operation. Although this should cause node 164 to follow Vdd 124as the power supply voltage rises, a moderate amount of supply noise ortransistor imbalance can falsely activate the latch, causing the powersupply to be clamped as though it were an ESD event. There is a similarproblem with the circuit 200 of FIG. 2, whereby the node 262 remains atthe Vdd potential during a normal power supply ramp-up operation.

In both of the conventional circuits 100 and 200, false activation ofthe clamp circuit in normal operation is destructive to the circuit.Furthermore, since manufacturing thresholds may vary based on operatingconditions, the circuits 100 and 200 may fail to power up correctly.

SUMMARY OF EMBODIMENTS OF THE PRESENT INVENTION

Electronic component protection power supply clamp circuits comprising aplurality of PMOS and NMOS transistors are described. These clampcircuits use a feedback latching circuit to retain an ESD-triggeredstate and efficiently conduct ESD current that has been diverted intothe power supply, in order to dissipate ESD energy. The feedbacklatching circuit also maintains a clamp transistor in its off state ifthe clamp circuit powers up untriggered, thus enhancing the clampcircuit's immunity to noise during normal operation. Passive resistanceinitialization of key nodes to an untriggered state, as well as passiveresistance gate input loading of a large ESD clamping transistor,further enhances the clamp circuit's immunity to false triggering acrossprocess and temperature variation. This also lengthens the time that theclamp circuit remains in the ESD-triggered state during human body model(HBM) or other long duration detected ESD events, causing the clamp todissipate all residual energy within the HBM ESD pulse and avoiding arise in post-ESD supply voltage that would otherwise pose a circuitreliability threat.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows an example of a conventional electronic componentprotection power supply clamp circuit;

FIG. 2 shows an example of an alternative conventional electroniccomponent protection power supply clamp circuit;

FIG. 3 is a schematic of a first embodiment of an electronic componentprotection power supply clamp circuit; and

FIG. 4 is a schematic of a second embodiment of an electronic componentprotection power supply clamp circuit.

DETAILED DESCRIPTION

Embodiments of the present invention use a circuit design that addressesthe concerns set forth above. In addition to using a latching circuit toretain an ESD-triggered state, these embodiments may optionally containone or more of the following additional features:

1) A latching circuit to maintain a clamp in its off state if thecircuit powers up untriggered. This improves the circuit's immunity tonoise in normal operation.

2) Passive resistance initialization of key nodes to an untriggeredstate is used to improve the circuit's immunity to false triggeringacross process and temperature variation.

3) Passive resistance gate input loading of a large ESD clampingtransistor is used to improve the circuit's immunity to false triggeringacross process and temperature variation. This improves the duration ofthe ESD state when detected from an HBM or other long duration ESDevent, clamping so that residual HBM ESD energy at the end of the eventdoes not cause an excess post-ESD supply voltage excursion that poses acircuit reliability threat.

FIG. 3 is a schematic of a first embodiment of an electronic componentprotection power supply clamp circuit 300. Circuit 300 includes acapacitor 302, resistors 304, 306 and 308, a diode 310, PMOS transistors312, 314 and 316, and NMOS transistors 318, 320, 322 and 324. Each ofthese components is connected to at least one of a Vss 326 or a Vdd 328.PMOS transistor 312 includes a gate terminal 330, a source terminal 332and a drain terminal 334. PMOS transistor 314 includes a gate terminal336, a source terminal 338 and a drain terminal 340. PMOS transistor 316includes a gate terminal 342, a source terminal 344 and a drain terminal346. NMOS transistor 318 includes a gate terminal 348, a source terminal350 and a drain terminal 352. NMOS transistor 320 includes a gateterminal 354, a source terminal 356 and a drain terminal 358. NMOStransistor 322 includes a gate terminal 360, a source terminal 362 and adrain terminal 364. NMOS transistor 324 serves as a clamp transistorthat includes a gate terminal 366, a source terminal 368 and a drainterminal 370. The source terminals 350, 356, 362 and 368 are connectedto Vss 326. The source terminals 332, 338 and 344, and the drainterminal 370, are connected to Vdd 328. Although the transistors used inthe circuit 300 are specified as being an NMOS transistor or a PMOStransistor, one skilled in the art would realize that any type oftransistor may be used.

As shown in FIG. 3, capacitor 302 has a first end that is connected toVdd 328, and a second end that is connected to node 372. The resistor304 has a first end that is connected to Vss 326, and a second end thatis connected to node 372. The resistor 306 has a first end that isconnected to Vdd 328, and a second end that is connected to a node 374.The resistor 308 has a first end that is connected to Vss 326, and asecond end that is connected to a node 376. The diode 310 includes ananode 378 that is connected to Vss 326, and a cathode 380 that isconnected to Vdd 328. The node 372 is also connected to the gateterminal 336 of the PMOS transistor 314, the gate terminal 354 of theNMOS transistor 320, the drain terminal 334 of the PMOS transistor 312,and the drain terminal 352 of the NMOS transistor 318. The node 374 isalso connected to the drain terminal 340 of the PMOS transistor 314, thedrain terminal 358 of the NMOS transistor 320, the gate terminal 330 ofthe PMOS transistor 312, the gate terminal 342 of the PMOS transistor316, the gate terminal 348 of the NMOS transistor 318, and the gateterminal 360 of the NMOS transistor 322. The node 376 also connectstogether the drain terminal 346 of the PMOS transistor 316, the drainterminal 364 of the NMOS transistor 322, and the gate terminal 366 ofthe NMOS transistor 324.

The circuit 300 of FIG. 3 comprises an RC circuit 382, formed bycapacitor 302 and resistor 304, which provides an RC differentiatingtrigger having a predetermined time constant, (for example, at least 75nanoseconds at node 372). For an ESD event state, the RC circuit 382outputs a logic high that drives two inverters: a first inverter 384including the transistors 314 and 320, and a second inverter 386including the transistors 316 and 322, leading into the NMOS transistor324, which creates a low-resistance ESD shunt between Vss 326 and Vdd328. Although the circuit 300 shown in FIG. 3 only includes twoinverters, any even total number of inverters, (e.g., 2, 4 or 6inverters), may be used. PMOS transistor 312 and NMOS transistor 318serve as a full feedback latching circuit 388. Under an ESD-inducedrapid supply ramp transient, capacitor 302 holds the node 372 to a logichigh voltage, driving node 374 to a logic low voltage through NMOStransistor 320. The logic low voltage on the node 374 cause PMOStransistor 312 to conduct, which holds node 372 to a logic high, as longas the effective resistance of the PMOS transistor 312 is much lowerthan that of the resistor 304 in the RC circuit 382. In this manner, theRC time constant only needs to be long enough to detect a rapid supplyramping of the ESD event state.

In accordance with this embodiment, the NMOS transistor 318 is used tomaintain clamp transistor 324 in its off state under normal operatingconditions, thus significantly improving immunity of the circuit 300 topower supply noise. In the off state, node 372 is essentially charged toVss 326, and node 374 is pulled to Vdd 328. Without transistor 318, thecapacitor 302 would trigger an ESD event state detection through theinverter 384 for a large enough positive noise event on Vdd 328. Thetransistor 318 decreases the effective resistance between node 372 andVss 326, thus causing node 372 to track the Vss 326 voltage during anormal operation noise event.

The resistor 306, connected between node 374 and Vdd 328, improves theimmunity of the circuit 300 to false triggering during a power supplyramp-up operation. Without the resistor 306, as the power supply rampsup slowly from a zero-volt level, the inverters 384 and 386 and thefeedback latching circuit 388 operate in an undefined state until thepower supply reaches a voltage level greater than the larger of the PMOSand NMOS transistor threshold voltages. Under certain NMOS/PMOStransistor skew and local mismatch conditions, the threshold voltages ofthe inverters 384 and 386 in the circuit 300 may be different, causingthe feedback latching circuit 388 to capture a falsely triggeredcondition before the inverter 384 drives the turned-off condition.Without resistor 306, the circuit 300 would be particularly susceptibleto this effect after aging-induced threshold voltage shifts from NBTIand PBTI. Because resistor 306 has no threshold voltage, it controls thevoltage of node 374 from the very beginning of a normal power supplyramp, predisposing the circuit 300 to operate in the turned-off state.

The resistor 308, connected between node 376 and Vss 326, preventstransistor 324 from clamping during a power supply ramp on Vdd 328.Additionally, resistor 308 causes the voltage at node 376 to drop belowVdd 328 as an HBM discharge progresses far into the tail of its decay,causing Vdd 328 to remain above the operating voltage for anESD-triggered state latch at nodes 372 and 374, the feedback latchingcircuit 388 and inverter 384. When inverter 386 has insufficient voltagerelative to transistor thresholds to operate, resistor 308 causes thevoltage at node 376 to decrease, preventing Vdd 328 from furtherdecreasing. This continues until there is so little energy remaining inHBM capacitance that the latch state is lost, and node 374 returns tothe Vdd 328 voltage, causing clamping to stop. At this point, there istoo little ESD energy remaining to raise Vdd 328 to a level that poses areliability risk, thus keeping electronic components safe fromovervoltage damage.

Alternatively, a PMOS transistor may be used as the clamp transistor 324instead of an NMOS transistor, whereby the resistor 308 would beconnected between node 376 and Vdd 328, instead of between node 376 andVss 326.

FIG. 4 is a schematic of a second embodiment of an electronic componentprotection power supply clamp circuit 400. The circuit 400 includes acapacitor 402, resistors 404, 406 and 408, a diode 410, PMOS transistors412, 414, 416 and 418, and NMOS transistors 420, 422, 424, 426 and 428.Each of these components is connected to at least one of Vss 430 or Vdd432. PMOS transistor 412 includes a gate terminal 434, a source terminal436 and a drain terminal 438. PMOS transistor 414 includes a gateterminal 440, a source terminal 442 and a drain terminal 444. PMOStransistor 416 includes a gate terminal 446, a source terminal 448 and adrain terminal 450. PMOS transistor 418 includes a gate terminal 452, asource terminal 454 and a drain terminal 456. NMOS transistor 420includes a gate terminal 458, a source terminal 460 and a drain terminal462. NMOS transistor 422 includes a gate terminal 464, a source terminal466 and a drain terminal 468. NMOS transistor 424 includes a gateterminal 470, a source terminal 472 and a drain terminal 474. NMOStransistor 426 includes a gate terminal 476, a source terminal 478 and adrain terminal 480. NMOS transistor 428 serves as a clamp transistorthat includes a gate terminal 482, a source terminal 484 and a drainterminal 486. Source terminals 460, 466, 472, 478 and 484 are connectedto Vss 430. Source terminals 436, 442, 448 and 454, and drain terminal486 are connected to Vdd 432. Although the transistors used in thecircuit 400 are specified as being an NMOS transistor or a PMOStransistor, one skilled in the art would realize that any type oftransistor may be used.

As shown in FIG. 4, the capacitor 402 has a first end that is connectedto Vss 430, and a second end that is connected to a node 488. Theresistor 404 has a first end that is connected to the Vdd 432, and asecond end that is connected to node 488. The resistor 406 has a firstend that is connected to the Vss 430, and a second end that is connectedto a node 490. The resistor 408 has a first end that is connected to theVss 430, and a second end that is connected to a node 494. The diode 410includes an anode 496 that is connected to Vss 430, and a cathode 498that is connected to Vdd 432. The node 488 is also connected to the gateterminal 440 of PMOS transistor 414, the gate terminal 464 of NMOStransistor 422, the drain terminal 438 of PMOS transistor 412, and thedrain terminal 462 of NMOS transistor 420. The node 490 is alsoconnected to the drain terminal 444 of PMOS transistor 414, the drainterminal 468 of NMOS transistor 322, the gate terminal 434 of PMOStransistor 412, the gate terminal 446 of PMOS transistor 416, the gateterminal 458 of NMOS transistor 420, and the gate terminal 470 of NMOStransistor 424. A node 492 connects together the drain terminal 450 ofPMOS transistor 416, the drain terminal 474 of NMOS transistor 424, thegate terminal 452 of PMOS transistor 418, and the gate terminal 476 ofNMOS transistor 426. The node 494 is also connected to the drainterminal 456 of PMOS transistor 418, the drain terminal 480 of NMOStransistor 426, and the gate terminal 482 of NMOS transistor 428.

The circuit 400 of FIG. 4 comprises an RC circuit 502, formed bycapacitor 402 and resistor 404, which provide an RC differentiatingtrigger having a predetermined time constant, (for example, at least 75nanoseconds at node 488). When triggered into an ESD event state, RCcircuit 502 outputs a logic low that drives three inverters: a firstinverter 504 including transistors 414 and 422, a second inverter 506including transistors 416 and 424, and a third inverter 508 includingtransistors 418 and 426, leading into NMOS transistor 428, which createsa low-resistance ESD shunt between Vss 430 and Vdd 432. Although thecircuit 400 shown in FIG. 4 only includes three inverters, any odd totalnumber of inverters, (e.g., 3, 5 or 7 inverters), may be used. PMOStransistor 412 and NMOS transistor 420 serve as a full feedback latchingcircuit 510. Under an ESD-induced rapid supply ramp transient, capacitor402 holds node 488 to a logic low voltage, driving node 490 to a logichigh voltage through PMOS transistor 414. The logic high voltage on node490 enables NMOS transistor 420, which holds node 488 to a logic low, aslong as the effective resistance of the NMOS transistor 420 is muchlower than that of resistor 404 in RC circuit 502. In this manner, theRC time constant only needs to be long enough to detect rapid supplyramping of the ESD event state.

In accordance with this embodiment, the PMOS transistor 412 is used tomaintain clamp transistor 428 in its off state under normal operatingconditions, thus significantly improving immunity of the circuit 400 topower supply noise. In the off state, node 488 is essentially charged toVdd 432, and node 490 is pulled to Vss 430. Without transistor 412, thecapacitor 402 would trigger an ESD event state detection through theinverter 504 for a large enough positive noise event on Vdd 432. Thetransistor 412 decreases the effective resistance between node 488 andVdd 422, thus causing node 488 to track the Vdd 432 voltage during anormal operation noise event.

The resistor 406, connected between node 490 and Vss 432, improves theimmunity of the circuit 400 to false triggering during a power supplyramp-up operation. Without the resistor 406, as the power supply rampsup slowly from a zero-volt level, the inverters 504, 506 and 508, andthe feedback latching circuit 510 in the circuit 400 operate in anundefined state until the power supply reaches a level greater than thelarger of the PMOS and NMOS transistor threshold voltages. Under certainNMOS/PMOS transistor skew and local mismatch conditions, the thresholdvoltages of the inverters 504, 506 and 508 may be different, causing thefeedback latching circuit 510 to capture a falsely triggered conditionbefore the inverter 504 drives the turned-off condition through theinverter chain. Without resistor 406, the circuit 400 would beparticularly susceptible to this effect after aging-induced thresholdvoltage shifts from NBTI and PBTI. Because resistor 406 has no thresholdvoltage, it controls the voltage of the node 490 from the very beginningof a normal power supply ramp, predisposing the circuit 400 to operatein the turned-off state.

The resistor 408, connected between node 494 and Vss 430, preventstransistor 428 from clamping during power supply ramp on Vdd 432.Additionally, resistor 408 causes the voltage at node 494 to drop belowVdd 432 as an HBM discharge progresses far into the tail of its decay,causing Vdd 432 to remain above the operating voltage for anESD-triggered state latch at nodes 488 and 490, the feedback latchingcircuit 510 and inverter 504. When inverter 508 has insufficient voltagerelative to transistor thresholds to operate, resistor 408 causes thevoltage at node 494 to decrease, preventing Vdd 432 from furtherdecreasing. This continues until there is so little energy remaining inHBM capacitance that the latch state is lost, and node 490 returns tothe Vss 430 voltage, causing clamping to stop. At this point, there istoo little ESD energy remaining to raise Vdd 432 to a level that poses areliability risk, thus keeping electronic components safe fromovervoltage damage.

Alternatively, a PMOS transistor may be used as the clamp transistor 428instead of an NMOS transistor, whereby the resistor 408 would beconnected between node 494 and Vdd 432, instead of between node 494 andVss 430. Furthermore, a passive initialization resistor, (in addition toresistors 404, 406 and 408), may optionally be connected between node492 and Vdd 432.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The circuits described herein may bemanufactured by using a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor.

Embodiments of the present invention may be represented as instructionsand data stored in a computer-readable storage medium. For example,aspects of the present invention may be implemented using Verilog, whichis a hardware description language (HDL). When processed, Verilog datainstructions may generate other intermediary data, (e.g., netlists, GDSdata, or the like), that may be used to perform a manufacturing processimplemented in a semiconductor fabrication facility. The manufacturingprocess may be adapted to manufacture semiconductor devices (e.g.,processors) that embody various aspects of the present invention.

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, agraphics processing unit (GPU), a DSP core, a controller, amicrocontroller, application specific integrated circuits (ASICs), fieldprogrammable gate arrays (FPGAs), any other type of integrated circuit(IC), and/or a state machine.

What is claimed is:
 1. An electronic component protection power supplyclamp circuit connected to a positive terminal and a negative terminalof a power supply, the clamp circuit comprising: a feedback latchingcircuit including a first p-type metal-oxide-semiconductor (PMOS)transistor and a first n-type metal-oxide-semiconductor (NMOS)transistor; a clamp transistor; a capacitor having a first end that isconnected to the negative power supply terminal, and a second end thatis connected to a drain terminal of the first PMOS transistor and adrain terminal of the first NMOS transistor; a first resistor having afirst end that is connected to the positive power supply terminal, and asecond end that is connected to the second end of the capacitor; aplurality of inverters connected between the second end of the firstresistor and a gate terminal of the clamp transistor; a second resistorhaving a first end that is connected to the negative power supplyterminal, and a second end that is connected to a gate terminal of thefirst PMOS transistor and a gate terminal of the first NMOS transistor;and a third resistor having a first end that is connected to either thepositive or negative power supply terminal, and a second end that isconnected to the gate terminal of the clamp transistor.
 2. The clampcircuit of claim 1 further comprising a diode having an anode that isconnected to the negative power supply terminal, and a cathode that isconnected to the positive power supply terminal.
 3. The clamp circuit ofclaim 1 wherein the inverters include: a first inverter including asecond PMOS transistor and a second NMOS transistor; a second inverterincluding a third PMOS transistor and a third NMOS transistor; and athird inverter including a fourth PMOS transistor and a fourth NMOStransistor, wherein the second end of the third resistor is furtherconnected to a drain terminal of the fourth PMOS transistor, and a drainterminal of the fourth NMOS transistor.
 4. The clamp circuit of claim 3wherein a source terminal of each of the first, second, third and fourthPMOS transistors is connected to the positive power supply terminal. 5.The clamp circuit of claim 3 wherein a source terminal of each of thefirst, second, third and fourth NMOS transistors is connected to thenegative power supply terminal.
 6. The clamp circuit of claim 3 whereinthe second end of the first resistor is further connected to a gateterminal of the second PMOS transistor and a gate terminal of the secondNMOS transistor.
 7. The clamp circuit of claim 3 wherein the second endof the second resistor is further connected to a drain terminal of thesecond PMOS transistor, a drain terminal of the second NMOS transistor,a gate terminal of the third PMOS transistor and a gate terminal of thethird NMOS transistor.
 8. The clamp circuit of claim 3 wherein a drainterminal of the third PMOS transistor is connected to a drain terminalof the third NMOS transistor, a gate terminal of the fourth PMOStransistor and a gate terminal of the fourth NMOS transistor.
 9. Theclamp circuit of claim 8 further comprising a fourth resistor having afirst end that is connected to the positive power supply terminal and asecond end that is connected to the drain terminal of the third PMOStransistor.
 10. The clamp circuit of claim 1 wherein the third resistorprevents the clamp transistor from clamping during a power supplyramp-up at the positive power supply terminal.
 11. A computer-readablestorage medium configured to store a set of instructions used formanufacturing a semiconductor device, wherein the semiconductor devicecomprises: a feedback latching circuit including a p-typemetal-oxide-semiconductor (PMOS) transistor and an n-typemetal-oxide-semiconductor (NMOS) transistor; a clamp transistor; acapacitor having a first end that is connected to a negative terminal ofa power supply, and a second end that is connected to a drain terminalof the PMOS transistor and a drain terminal of the NMOS transistor; afirst resistor having a first end that is connected to a positiveterminal of the power supply, and a second end that is connected to thesecond end of the capacitor; a plurality of inverters connected betweenthe second end of the first resistor and a gate terminal of the clamptransistor; a second resistor having a first end that is connected tothe negative power supply terminal, and a second end that is connectedto a gate terminal of the PMOS transistor and a gate terminal of theNMOS transistor; and a third resistor having a first end that isconnected to either the positive or negative power supply terminal, anda second end that is connected to the gate terminal of the clamptransistor.
 12. The computer-readable storage medium of claim 11 whereinthe instructions are Verilog data instructions.
 13. Thecomputer-readable storage medium of claim 11 wherein the instructionsare hardware description language (HDL) instructions.